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Discussion Starter · #1 ·
G'day All

This is simpler-laymans talk, not strictly accurate, so please no-one shoot
me for using "bad" terminology. It is in response to the question: how come
there can be more amps in the motor than coming from the batteries?

First thing, a PWM (pulse width modulation) controller is one that varies
the on-time pulse width, be it a Curtis, Zilla, Raptor or an older design
SCR controller. A contactor controller almost always has the same amps in
the battery and motor wires.

A PWM controller has some kind of electronic switch in it that turns the
battery connection on and off. In an older SCR controller, it actually is
(on) same current in battery and in motor (off) no current from battery,
which is why SCR controllers are usually harder on batteries. (in a
transistorised controller,the controller has other components [capacitors]
that averages out the battery amps so that Nothing Bad happens).

OK, so the controller turns on, connecting the battery to the motor. Amps
starts to flow into the motor, and it is the same amps in the battery wire
as in the motor wires. A little bit of time later, the controller decides
that there is enough amps happening, so turns off the switch, so amps stops
flowing from the batteries. The current in the motor cannot 'just stop'
because it pushed up a magnetic field, and now that magnetic field starts
to fall back, keeping the amps going - this goes through the free-wheel
diodes in the controller. At some time depending on the controller design,
the controller switches back on, and amps again flow from the battery into
the motor.

If the controller has the amps coming from the battery at 10% on time, and
90% off time, the average amps from the batteries is only 10% of the amps
in the motor wires. You don't get something for nothing, the average motor
volts is only 10% that of the batteries.

Hope this is of help to someone.


[Technik] James

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